Lightweight high compressive strength drainage pipe

ABSTRACT

A corrugated plastic drainage pipe having a compressive strength of at least 1,000 pounds per linear foot and being of lightweight construction with a wall thickness no greater than about onesixteenth inch and wherein spaced apart successively arranged annular ribs with interconnecting annular valley portions therebetween define corrugations along the periphery of the pipe, the ribs and valley portions per foot each being about seventeen in number, the majority of the annular ribs being uninterrupted and arranged in spaced groups with an interrupted rib between adjacent groups, and each interrupted rib comprising a set of three interconnected circularly arranged spaced apart arcuate rib segments correspondingly arranged throughout the pipe, and one of the rib segments of each set being substantially longer than the other two rib segments and having an arcuate extent of at least 180 degrees.

[ Feb.5,197 l 1 LIGHTWEIGHT HIGH COMPRESSIVE STRENGTH DRAINAGE PIPE [75]Inventor: Ernest J. Maroschak, Roseboro,

[73] Assignee: Plastic Tubing, Inc., Roseboro, NC.

22 Filed: June 12, 1972 211 Appl. No.: 261,781

Related US. Application Data [63] Continuation-impart of Ser. No.228,508, Feb. 23,

[58] Field of Search 6l/10,1l, 12,13; 130/178, 130/121,-l05, 173

[56] 7 References Cited UNITED STATES PATENTS 3,658,097 4/1972 Martin etal. 138/121 3,605,817 9/1971 Bauman et al.... 138/121 1,875,395 9/1932Salisburym, 61/10 OTHER PUBLICATIONS l-lancor Sweets File 15,21 Han 1970Primary Examiner-Jacob Shapiro Attorney, Agent, or Firm-Parrott, Bell,Seltzer, Park & Gibson [57] TRACT A corrugated plastic drainage pipehaving a compressive strength of at least 1,000 pounds per linear footand being of lightweight construction with a wall thickness no greaterthan about one-sixteenth inch and wherein spaced apart successivelyarranged annular ribs with interconnecting annular valley portionstherebetween define corrugations along the periphery of the pipe, theribs and valley portions per foot each being about seventeen in number,the majority of the annular ribs being uninterrupted and arranged inspaced groups with an interrupted rib between adjacent group's, and eachinterrupted rib comprising a set of three interconnected circularlyarranged spaced apart arcuate rib segments correspondingly arrangedthroughout the pipe, and one of the rib segments of each set beingsubstantially longer than the other two rib segments and having anarcuate extent of at least 180 degrees.

14 Claims, 5 Drawing Figures PATENIEUFEB 51w 3789.615

O. DIVA LLE-Y I 1 LIGHTWEIGHT HIGH COMPRESSIVE STRENGTH DRAINAGE PIPEThis application is a continuation-in-part of my copending applicationSer. No. 228,508, filed Feb. 23, 1972 and entitled CORRUGATED DRAINAGEPIPE.

This invention relates to corrugated drainage pipes and, moreparticularly, to drainage pipes that are buried in the ground for usewith septic tanks, for example, and wherein the pipe is of lightweightconstruction with a wall thickness no greater than about one-sixteenthinch and has a compressive strength of at least 1,000 pounds per linearfoot to withstand compressive forces of heavy vehicles, for example,passing thereover.

The primary object of this invention is to provide an improvedcorrugated resilient plastic drainage pipe of lightweight constructionwherein the pipe is provided with annular ribs and interconnectingvalley portions arranged and so constructed to, provide a highcompressive strength to the pipe and wherein the wall thickness of thepipe is very thin so as to minimize the plastic material in the pipe andto obtain the lightweight construction.

A more specific object of this invention is to provide an improvedcorrugated resilient plastic drainage pipe having a compressive strengthof at least 1,000 pounds perIinear foot, with the pipe being oflightweight construction with a wall thickness no greater than aboutone-sixteenth inch and formed of a plastic material having a densitywithin the range of about 0.954 to 0.957 gm/cm so as to provide thedesired resiliency to the pipe while attaining the desired level ofcompressive strength therein and wherein the pipe has spaced apartsuccessively arranged annular ribs with interconnecting annular valleyportions therebetween defining corrugations along the periphery of thepipe, and wherein the ribs and valley portions per foot are each about17 in number, the majority of the annular ribs being uninterrupted andsuccessively arranged in spaced groups with an interrupted rib betweenadjacent groups, and wherein each interrupted rib comprises a set ofthree interconnected circularly arranged spaced apart arcuate ribsegments correspondingly arranged throughout the pipe, and one ribsegment of each set being substantially longer than the other two ribsegments and having an arcuate extent of at least 180.

Some of the objects and advantages of the invention having been stated,others will appear as the description proceeds, when taken in connectionwith the accompanying drawing, in which FIG. I is an elevational viewofa length of corrugated drainage pipe in accordance with thisinvention, viewed from the bottom of the pipe;

FIG. 2 is a cross sectional view of the drainage pipe taken along line2-2 of FIG. 1;

FIG. 3 is a cross sectional view of the drainage pipe taken along line33 of FIG. 1;

FIG. 4 is a cross sectional view of the drainage pipe taken along line44 of FIG. 1; and

FIG. 5 is an enlarged fragmentary sectional view taken along line 5-5 ofFIG. 1 and illustrating the wall configuration of the drainage pipe.

Referring now more particularly to the drawing, reference numeralbroadly indicates a corrugated drainage pipe in accordance with thisinvention which is formed of a plastic material, such as polyethylene,

and wherein the wall thickness of the drainage pipe is no greater thanabout one-sixteenth inch.

Spaced apart annular ribs 11 are successively arranged in a uniformmanner throughout the length of the pipe and are interconnected byannular valley portions 12 positioned therebetween. As will be notedupon viewing FIG. I, wherein one linear foot of the pipe is identifiedtherein, the number of ribs and valley portions per linear foot are eachabout seventeen in number, with the majority of the annular ribs beinguninterrupted and successively arranged in spaced groups of five with aninterrupted rib 11' between adjacent groups.

Viewing the drainage pipe in terms of its repeat pattern, it will benoted that the ribs and valley portions are each approximately six innumber per each 4 inches of pipe length, with five of the six annularribs 11 being uninterrupted and successively arranged in a group andwherein the uninterrupted rib 11 is adjacent one end of the group.

Referring now to the interrupted ribs, it will be noted that eachinterrupted rib 11 comprises a set of three circularly arranged spacedapart arcuate rib segments, as indicated by numerals 14, 15 and 16,respectively, with the respective rib segments forming each of theinterrupted ribs 11 being correspondingly arranged throughout the pipeso as to be in longitudinal alignment with each other.

Between the ends of arcuate rib segments 14, l5, 16 is a series of threedrainage holes identified at 20, 20a and 20b, which series of holes, asillustrated, is arcuately arranged. The series of drainage holes 20, 20aand 20b are located around the bottom half of the pipe, when the pipe isproperly installed in the ground, so that the rib segments 14, 15, 16projecting outwardly therefrom serve to space the holes from the earthfor effecting proper drainage therethrough. Furthermore, it will benoted that the rib segment 14 is desirably longer than the other twosegments and has an arcuate extent encompassing at least the upper half-of the drainage pipe, i.e., at least and preferably is of an extent ofat least 200 to 220 so as to shieldingly protect drainage holes 20 and20b during the backfilling of the earth around the drainage pipe toavoid blocking the holes.

For aiding in properly installing the drainage pipe, sight means 30(FIG. 4) is preferably provided longitudinally of the pipe along thesurface thereof in direct opposition-to drainage hole 20a for visuallyaiding in installing the pipe in the ground'with the drainage holesproperly positioned lowermost. As illustrated, sight means 30 is in theform of a painted line contrasting with the color of the drainage pipebut may, if desired, be in the form of a series of small rib portionsextending longitudinally of the pipe along the outer surface of theannular ribs 11.

Referring now more particularly to the set of arcuate rib segments 14,15, 16, which comprise each of the interrupted ribs 11, as notedearlier, rib segment 14 is desirably of an arcuate extent exceeding 180,for shieldingly protecting the drainage holes. The shorter rib segments15 and 16 are preferably of the same length as each other and each, asillustrated, has an arcuate extent of about 40 to 45. Preferably, asillustrated, the respective arcuate segments l4, l5, 16 are uniformlyspaced from each other so as to readily accommodate similar sizedrainage holes therebetween,

which drainage holes are of at least /2 inch diameter and preferably ofabout /4 inch diameter. The drainage holes each extend through anarcuate extent of the pipe of about 15 to 25 and have a diameter greaterthan the width of the ribs. As illustrated in FIG. 4, intersecting axesof adjacent drainage holes define an included angle of about 60 asindicated at A.

Referring now more particularly to the detail construction andarrangement of the ribs 11 and interconnecting valley portions 12, itwill be noted that the drawing illustrates a nominal 4 inch corrugateddrainage pipe made in accordance with this invention. However, it is tobe understood that the constructional features of the invention may beembodied in a variety of pipe sizes such as nominal 5 and 6 inchdiameter pipes with the only appreciable difference being in the overallweight per unit of length. The 4 inch pipe, as illustrated in FIG. 3,has an internal diameter of 3.916 inches measured interiorly of thevalleys 12, and an external diameter of 4.566 inches. This 4 inchdiameter pipe embodiment of the invention has a weight of no more thanabout 6 ounces per linear foot and preferably approximately 5- /2 ouncesper linear foot as presently being commercialized. As indicated earlier,the compressive strength of the pipe is at least 1,000 pounds per linearfoot and tests have indicated that the compressive strength falls withina range of about 1,000 to 1,100 pounds per linear foot even after thedrainage holes have been drilled therein. In this respect, it has beendetermined that about 3 percent of the weight of the pipe is lostthrough the drilling of the nine holes per foot therein and that thethree percent loss in weight is almost directly correlated to a threepercent reduction in the compressive strength of the product followingdrilling. Thus, the corrugated drainage pipe may be viewed as having a 3percent higher compressive strength when tested prior to the holes beingdrilled therein but, the compressive strength is always at least 1,000pounds per linear foot, even after the holes are provided.

At this point, it is believed to be helpful to briefly outline the typeof standard test that is employed in determining the compressivestrength of the drainage pipe. The test equipment involves positioning al-foot length of the pipe between a movable l-foot long pressure plateand a back-up plate with 2 inches of sand surrounding the pipe. When1,000 pounds of pressure is applied to the pressure plate, a lateralcompressive force is applied to the pipe, and in the event the diameterof the pipe is reduced no more than 1 inch by the compressive force, thepipe has passed the test. It is understood that this type of test is astandard test for pipe having a diameter of 4 to 6 inches.

It has been determined from compressive tests that, if the density ofthe polyethylene plastic material falls below the range of about 0.954to 0.957 gm/cm the pipe would undesirably be too flexible and springyand normally would not pass the compressive strength test of 1,000pounds per linear foot. Also, it has been determined by similar teststhat, if the density goes above Said range 9t.!2 Q- 5.. IQ9- l l 1l Pherirewflk tddi'i'ffihd brittle and would be most difficult to handleand would readily crack in cold weather, particularly when beinguncoiled from a coiled package.

Referring more particularly to the details of the configuration of theribs and valleys, and wall thicknesses thereof, it is to be noted, asbest illustrated in FIG. 5,

that the ribs 11 are wider than the valley portions 12 interconnectingthe same and also that the height of the ribs is greater than the widthof the valley portions. This arrangement considered with the earliermentioned number of ribs and valley portions per unit of length of pipecontributes to the high compressive strength of the pipe even though, asearlier noted, the wall thickness is no greater than about one-sixteenthinch. For a more specific comparison, it is to be noted that all theribs have a width of approximately one-half inch, the width beingdetermined by adding the width of the periphery of the ribs plus thewidth of the said walls thereof taken in a straight line, namely, asillustrated in FIG. 5, adding 0.289 (2 X 0.113) 0.515. As illustrated,the height of the ribs when measured from the annular valleys 12 is0.270 inch. The width of the annular valleys l2 taken to the juncturewith the side walls 1.1a of the ribs is 0.187 inch, as illustrated.

It will further be noted, as best illustrated in FIG. 5, that smallannular reinforcing beads 11b are provided along opposite sides of eachof the said annular ribs closely adjacent the periphery thereof. It hasbeen determined that these annular beads enhance the compressivestrength of the pipe by providing thickened rib wall portions servingsomewhat analogous to reinforcing rings. It will further be noted thatthe thickest wall portion of the pipe is through the medial portions ofthe valleys 12 with the thickness thereof being 0.055 inch. Further, itwill be noted that the thinnest wall portion is defined by the sidewalls 11a of the ribs 11, which are 0.043 inches. Further, it will benoted that an intermediate wall thickness of 0.048 inches is present inthe outer wall portions of the ribs 11. It is also noted that theinterior surfaces of said annular valley portions 12 are crowned orcurved to further contribute to the desired compressive strengthcharacteristics of the product. Also, the peripheries of the ribs 11,for similar reasons, are crowned.

Thus, it will be noted that this thus described and illustrated 4 inchdiameter pipe embodiment of the invention has a wall thickness nogreater than about onesixteenth inch and preferably within the range ofabout 0.043 to 0.055 inches, as presently being commercialized, andwherein the same is desirably formed of polyethylene plastic material.

It should thus be apparent from the foregoing that the instant inventionpermits obtaining a high compressive strength corrugated plasticdrainage pipe with a small quantity of plastic material due to themanner in which the pipe is constructed.

In the drawing and specification, there has been set forth a preferredembodiment of the invention, and although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

What is claimed is:

1. A corrugated resilient plastic drainage pipe having a compressivestrength of-at least 1,000 pounds per linear foot and being oflightweight construction with a wall thickness no greater than aboutone-sixteenth inch and weighing no more than about 6 ounces per linearfoot, said pipe having spaced apart successively arranged annular ribswith interconnecting annular valley portions therebetween definingcorrugations along the periphery of the pipe and wherein the interiorsurfaces of said annular valley portions are crowned and the wallthickness of the medial areas of said annular valley other two ribsegments and having an arcuate extent of at least 180, the other two ribsegments being of substantially equal length.

2. A corrugated resilient plastic drainage pipe according to claim 1,wherein said ribs are wider than said valley portions interconnectingthe same and wherein the height of said ribs is also greater than thewidth of the valley portions.

3. A corrugated resilient plastic drainage pipe according to claim 1,wherein the wall thickness of the medial areas of said annular valleyportions is of about 0.055 inch. 7

4. A corrugated resilient plastic drainage pipe according to claim 1,wherein relatively small annular reinforcing beads are provided alongopposite sides of each of said annular ribs closely adjacent theperiphery thereof.

5. A corrugated resilient plastic drainage pipe according to claim 1,wherein the interior diameter of the pipe is approximately 4 inches andthe exterior diameter is approximately 4 /2 inches and wherein theperipheries of the annular ribs are crowned.

6. A corrugated resilient plastic drainage pipe according to claim 1,wherein a series of three drainage holes are provided between said ribsegments of each set with the diameter ofthe holes being greater thanthe width of the ribs, two of said drainage holes being positionedbetween the opposite terminal ends of said long rib segment and therespective shorter rib segments, the third drainage hole beingpositioned between the shorter rib segments and being substantiallycentrally disposed between said two holes, and means extendinglongitudinally of said pipe along the outer surface thereof directlyopposite said third drainage holes for visually aiding in installing thepipe in the ground with all of the drainage holes located below thehorizontal centerline of the pipe and the third drainage holes occupyinglowermost position.

7. A corrugated resilient plastic drainage pipe having a compressivestrength of at least 1,000 pounds per linear foot and being oflightweight construction of a plastic material having a density withinthe range of about 0.954 to 0.957 gm/cm with a wall thickness no greaterthan about one-sixtheenth inch, said pipe having spaced apartsuccessively arranged annular ribs with interconnecting annular valleyportions therebetween defining corrugations along the periphery of thepipe and wherein the interior surfaces of said annular valley portionsare crowned and the wall thickness of the medial areas of said annularvalley portions is greater than any other wall portion of thecorrugations of the pipe, and wherein the ribs and valley portions perfoot are each about 17 in number, the majority of said annular ribsbeing uninterrupted and successively arranged in spaced groups of fivewith an interrupted rib between adjacent groups, each interrupted ribcomprising a set of three interconnected circularly arranged spacedapart arcuate rib segments correspondingly arranged throughout the pipe,and one rib segment of each set being substantially longer than theother two rib segments and having an arcuate extent of at least 180, theother two rib segments being of substantially equal length.

8. A corrugated resilient plastic drainage pipe according to claim 7,wherein the interior diameter of the pipe is approximately 4 inches andthe exterior diameter of the pipe is approximately 4% inches, andwherein the pipe weighs no more than about 6 ounces per linear foot.

9. A corrugated resilient plastic drainage pipe according to claim 7,wherein the wall thickness of the pipe is within the range of about0.043 to 0.055 inch and the plastic material is polyethylene.

10. A corrugated resilient plastic drainage pipe according to claim 7,wherein the pipe weighs no more than 5 /2 ounces per linear foot andwherein the plastic material is polyethylene having a density of 0.955gm/cm.

11. A corrugated resilient plastic drainage pipe according to claim 7,wherein said ribs are wider than said valley portions interconnectingthe same and wherein the height of said ribs is also greater than thewidth of the valley portions.

12. A corrugated resilient plastic drainage pipe according to claim 7,wherein a series of three drainage holes are provided between said ribsegments of each set with the diameter of the holes being greater thanthe width of the ribs, two of said drainage holes being positionedbetween the opposite terminal ends of said long rib segment and therespective shorter rib segments, and the third drainage hole beingpositioned between the shorter rib segments and being substantiallycentrally disposed between said two holes.

13. A corrugated resilient plastic drainage pipe having a compressivestrength of at least 1,000 pounds per linear foot and being oflightweight construction of a plastic material having a density withinthe range of about 0.954 to 0.957 gm/cm with a wall thickness no greaterthan about one-sixteenth inch, said pipe having' spaced apartsuccessively arranged annular ribs with interconnecting annular valleyportions therebetween defining corrugations along the periphery ofthepipe and wherein the interior surfaces of said annular valleyportions are crowned and the wall thickness of the medial areas of saidannular valley portions is greater than any other wall portion of thecorrugations of the pipe, and wherein the ribs and valley portions areapproximately six in number per each 4 inches of pipe length, five ofsaid six annular ribs being successively arranged in a group with aninterrupted rib adjacent one end of the group, each interrupted ribcomprising a set of three interconnected circularly arranged spacedapart arcuate rib segments correspondingly arranged throughout the pipe,and one rib segment of each set being substantially longer than theother two rib segments and having an arcuate extent of at least 180, theother two rib segments being of substantially equal length.

14. A corrugated resilient plastic drainage pipe having a compressivestrength of at least 1,000 pounds per linear foot and being oflightweight construction with a wall thickness no greater than aboutone-sixteenth inch and weighing no more than about 6 ounces per linearfoot, said pipe having spaced apart successively arof threeinterconnected circularly arranged spaced apart arcuate rib segmentscorrespondingly arranged throughout the pipe, and one rib segment ofeach set being substantially longer than the other two rib segments andhaving an arcuate extent of at least the other two rib segments being ofsubstantially equal length.

1. A corrugated resilient plastic drainage pipe having a compressivestrength of at least 1,000 pounds per linear foot and being oflightweight construction with a wall thickness no greater than aboutone-sixteenth inch and weighing no more than about 6 ounces per linearfoot, said pipe having spaced apart successively arranged annular ribswith interconnecting annular valley portions therebetween definingcorrugations along the periphery of the pipe and wherein the interiorsurfaces of said annular valley portions are crowned and the wallthickness of the medial areas of said annular valley portions is greaterthan any other wall portion of the corrugations of the pipe, and whereinthe ribs and valley portions per foot are each about 17 in number, themajority of said annular ribs being uninterruptEd and successivelyarranged in spaced groups with an interrupted rib between adjacentgroups, each interrupted rib comprising a set of three interconnectedcircularly arranged spaced apart arcuate rib segments correspondinglyarranged throughout the pipe, and one rib segment of each set beingsubstantially longer than the other two rib segments and having anarcuate extent of at least 180*, the other two rib segments being ofsubstantially equal length.
 2. A corrugated resilient plastic drainagepipe according to claim 1, wherein said ribs are wider than said valleyportions interconnecting the same and wherein the height of said ribs isalso greater than the width of the valley portions.
 3. A corrugatedresilient plastic drainage pipe according to claim 1, wherein the wallthickness of the medial areas of said annular valley portions is ofabout 0.055 inch.
 4. A corrugated resilient plastic drainage pipeaccording to claim 1, wherein relatively small annular reinforcing beadsare provided along opposite sides of each of said annular ribs closelyadjacent the periphery thereof.
 5. A corrugated resilient plasticdrainage pipe according to claim 1, wherein the interior diameter of thepipe is approximately 4 inches and the exterior diameter isapproximately 4 1/2 inches and wherein the peripheries of the annularribs are crowned.
 6. A corrugated resilient plastic drainage pipeaccording to claim 1, wherein a series of three drainage holes areprovided between said rib segments of each set with the diameter of theholes being greater than the width of the ribs, two of said drainageholes being positioned between the opposite terminal ends of said longrib segment and the respective shorter rib segments, the third drainagehole being positioned between the shorter rib segments and beingsubstantially centrally disposed between said two holes, and meansextending longitudinally of said pipe along the outer surface thereofdirectly opposite said third drainage holes for visually aiding ininstalling the pipe in the ground with all of the drainage holes locatedbelow the horizontal centerline of the pipe and the third drainage holesoccupying lowermost position.
 7. A corrugated resilient plastic drainagepipe having a compressive strength of at least 1,000 pounds per linearfoot and being of lightweight construction of a plastic material havinga density within the range of about 0.954 to 0.957 gm/cm3 with a wallthickness no greater than about one-sixtheenth inch, said pipe havingspaced apart successively arranged annular ribs with interconnectingannular valley portions therebetween defining corrugations along theperiphery of the pipe and wherein the interior surfaces of said annularvalley portions are crowned and the wall thickness of the medial areasof said annular valley portions is greater than any other wall portionof the corrugations of the pipe, and wherein the ribs and valleyportions per foot are each about 17 in number, the majority of saidannular ribs being uninterrupted and successively arranged in spacedgroups of five with an interrupted rib between adjacent groups, eachinterrupted rib comprising a set of three interconnected circularlyarranged spaced apart arcuate rib segments correspondingly arrangedthroughout the pipe, and one rib segment of each set being substantiallylonger than the other two rib segments and having an arcuate extent ofat least 180*, the other two rib segments being of substantially equallength.
 8. A corrugated resilient plastic drainage pipe according toclaim 7, wherein the interior diameter of the pipe is approximately 4inches and the exterior diameter of the pipe is approximately 4 1/2inches, and wherein the pipe weighs no more than about 6 ounces perlinear foot.
 9. A corrugated resilient plastic drainage pipe accordingto claim 7, wherein the wall thickness of the pipe is within the rangeof about 0.043 to 0.055 inch and the plastic material is polyethylene.10. A corrugated resilient plastic drainage pipe according to claim 7,wherein the pipe weighs no more than 5 1/2 ounces per linear foot andwherein the plastic material is polyethylene having a density of 0.955gm/cm3.
 11. A corrugated resilient plastic drainage pipe according toclaim 7, wherein said ribs are wider than said valley portionsinterconnecting the same and wherein the height of said ribs is alsogreater than the width of the valley portions.
 12. A corrugatedresilient plastic drainage pipe according to claim 7, wherein a seriesof three drainage holes are provided between said rib segments of eachset with the diameter of the holes being greater than the width of theribs, two of said drainage holes being positioned between the oppositeterminal ends of said long rib segment and the respective shorter ribsegments, and the third drainage hole being positioned between theshorter rib segments and being substantially centrally disposed betweensaid two holes.
 13. A corrugated resilient plastic drainage pipe havinga compressive strength of at least 1,000 pounds per linear foot andbeing of lightweight construction of a plastic material having a densitywithin the range of about 0.954 to 0.957 gm/cm3 with a wall thickness nogreater than about one-sixteenth inch, said pipe having spaced apartsuccessively arranged annular ribs with interconnecting annular valleyportions therebetween defining corrugations along the periphery of thepipe and wherein the interior surfaces of said annular valley portionsare crowned and the wall thickness of the medial areas of said annularvalley portions is greater than any other wall portion of thecorrugations of the pipe, and wherein the ribs and valley portions areapproximately six in number per each 4 inches of pipe length, five ofsaid six annular ribs being successively arranged in a group with aninterrupted rib adjacent one end of the group, each interrupted ribcomprising a set of three interconnected circularly arranged spacedapart arcuate rib segments correspondingly arranged throughout the pipe,and one rib segment of each set being substantially longer than theother two rib segments and having an arcuate extent of at least 180*,the other two rib segments being of substantially equal length.
 14. Acorrugated resilient plastic drainage pipe having a compressive strengthof at least 1,000 pounds per linear foot and being of lightweightconstruction with a wall thickness no greater than about one-sixteenthinch and weighing no more than about 6 ounces per linear foot, said pipehaving spaced apart successively arranged annular ribs withinterconnecting annular valley portions therebetween definingcorrugations along the periphery of the pipe and wherein the interiorsurfaces of said annular valley portions are crowned and the wallthickness of the medial areas of said annular valley portions is greaterthan any other wall portion of the corrugations of the pipe, and whereinthe ribs and valley portions per foot are each about 17 in number, someof said ribs being interrupted and comprising a set of threeinterconnected circularly arranged spaced apart arcuate rib segmentscorrespondingly arranged throughout the pipe, and one rib segment ofeach set being substantially longer than the other two rib segments andhaving an arcuate extent of at least 180*, the other two rib segmentsbeing of substantially equal length.